Changes in milk plasminogen, plasmin and in vitro bacterial growth in whey during early lactation

The activity of milk plasmin, plasminogen and N-acetyl-beta-glucosaminidase (NAGase) and the trypsin-inhibitor capacity (TIC) were monitored in 40 quarters during the first month of lactation. TIC and NAGase activity decreased rapidly and plasmin activity more slowly during the first week. Conversely milk plasminogen increased as time elapsed from parturition. When the quality of whey was analysed as a growth medium for mastitis pathogens, a slight inhibition in the growth of Escherichia coli, Staphylococcus aureus and Streptococcus agalactiae was seen at the day of parturition. There was a distinct stimulatory effect on the growth of Str. agalactiae during the second week of lactation. No relationship was found between in vitro bacterial growth and respective plasmin or plasminogen activity in milk.